Sun Microsystems StorEdge Network Data Replicator 3 User Manual

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Network Data Replicator 3.0

Config uratio n Gui de

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Part No. 806-7550-10 June 2001, Revision A

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Please

Recycle

Preface v

1. Overview 1

Sun SND R Software Description 1 Supported Hardware an d Software 3

TCP/IP Connection Hardware Components 3

Network M ultipathing 4 Applications 5 Architecture 5

2. Configuration Considerations 7

Volumes Eligible fo r Replication 7

Choosing Volume Level Protection 8 Bitmap Vo lumes for Scoreboard Log s 8 Choosing a Connection Medium to Link My Sites 9

ATM Link Advantages 9

Configuring Redundant Links Bet ween Sites 10

Link Security 10 Choosing Be tween Synchr onous and Asynchronous Replicati on 11

When To Suspend Replication to th e Secondary Site 12

iii

Configuring The Sun SNDR Software for Mutual Replication 12 Order-Dependent Writes and Volume Set Grouping 13 Recovery Considerations 14

Failing Over to th e Secondary Site 14

Recovering the Primary or Secondary Site 14

Using The Sun SNDR and Sun StorEdge Instant Image Software 16 Sun SND R Software and Sun Sto rEdg e Fast Write Cache Software 17

One-to-Many and Multihop Volume Sets 18 Using The Sun SNDR Software in a Firewall Environment 19

iv Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Preface

The Sun StorEdge Network Data Replicator 3.0 Configuration Guide describes the Sun StorEdge™ Network Data Replicator (Sun SNDR) software and general information about its use. This guide is intended for system administrators who have experience with the Solaris™ operating environment and related di sk storage systems.

Before You Read T his Book

To f ully u se the info rmat ion in this document, you must have thorough knowledge of the topics discussed in these books:

■ Sun S torEdge Network Data Replicator 3.0 System Administrator’s Guide

■ Sun StorEdge Network Data Replicator 3.0 Installation Guide

■ Sun StorEdge Network Data Replicator 3.0 Release Notes

The Sun SNDR softwa re must be installed as described in the inst allation and release documentation.

Using UNIX Commands

This document may not contain in formation on basic UN IX®commands and procedures such as shutting down the system, booting the system, and configuring devices.

Refer to the software documentation that you received with your system.

Documentation Conventions

Typeface or Symbol Meaning Examples

AaBbCc123 The names of commands,

files, and directories; on-screen compu ter output.

AaBbCc123

AaBbCc123 Book titles, new words or

[ ] In syntax, brackets indi cate

{ arg | arg} In syntax, br aces and pipes

What you type, when contrasted wi th on-screen computer output .

terms, words to be emphasized. Command-line variable; replace with a real name or value.

that an argument is optional.

indicate that one of the arguments must be specified.

Edit your .login file. Use ls -a to list all files.

% You have mail. % su

Password:

Read Chapter 6 in the User’s Guide. These are called class options. You must be root to do this. To delete a file, type rm f ilen a m e.

scmadm [–d sec][–r n[:n][,n]...] [–z]

sndradm -b

{phost | shost}

vi Sun StorEdge Network Dat a Replicator 3.0 Configuration G uide • June 2001

Shell P romp t s

Shell Prompt

Cshell machine_name% Cshellsuperuser machine_name# Bourne shell and Korn shell $ Bourne shell and Korn shell superuser #

Accessing Sun D ocume nta tion Online

A broad selection of Sun system documentation is lo cate d at:

http://www.sun.com/products-n-solutions/hardware/docs

A compl ete set of Sola ri s documentati o n and many other titles are located at:

http://docs.sun.com

For the latest version of released storage sof tware documentatio n, go to:

http://www.sun.com/products-n-solutions/hardware/docs/Software/

Ordering Sun Do cumentation

For the latest version of storage software documentation, go to:

http://www.sun.com/products-n-solutions/hardware/docs/Software/

Fatbrain.com, an Internet professional bookstore, s tocks select product documentation from Sun Microsystems, Inc.

For a list of documents and how to order them, visit the Sun Documentation Center on Fatbrain.com at:

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Preface ix

x Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

CHAPTER

Overv iew

Caution – Do not install or use th e Sun StorEdge Version 3.0 Core a nd data s ervices

software on serve rs i n a Sun Cluster 3. 0 environment. Th e Version 3.0 software is not co-existent with the Sun Cluster 3.0 environment. The Version 3.0 software is

co-existent in the Sun Cluster 2.2 environment, where it will not interfere with failover. The Version 3.0 core and data servi ces software is cluster aware i n the Sun Cluster 3.0 Update 1 en vironment and provides high availability f or the Sun StorEdge software.

Sun SNDR Software Description

The Sun SDNR software is a remote replication facility for the Solaris™ operating

environment. It is intended for u se as part of a disaster recov ery and busin ess continuance plan to provide redundant storage of critica l information across physically sep arate sites. It is designed to be active during normal application access to the data volumes, and it will continually replicate the d ata to the remote site.

The Sun SDNR softw are en ables you to replicate d isk volumes between physically separate pri m a r y a nd secondar y hosts in real time . To transport da ta, the Sun SD NR software uses any Sun network adapter that supports TCP/IP.

The Sun SNDR software volume set consists of a primary v olume residing o n a local host and a secondary volume residing on a remo te host. The vo lume set also includes a bitmap volum e on each h ost to track w rite operations a nd differences between t he volumes.

Youcanupdatethedataonthesecondaryvolumebyissuingacommandto resynchronize the volumes. You can also restore data from the secondary volume to the primary volume b y issuing a command t o reverse resynchronize the volumes.

The replication mode ca n be synchronous or asynchronous based as a user-selectable parameter for each Sun SN DR volume set. ( Use the sndradm enable command and select the sync or async parameter Use the sndradm -R m command to change the replicati o n mode thereafter.) The vo lu m es can be upd ated synchronously in re al time or asynchronously using a store-and-forward techn ique .

Typically, a p rimary volume is first explicitly copied to a designated secondary volume to establish match ing contents. As applications write to the primary volum e, the Sun SDNR software replicates ch ang es to the secondary volume, keeping th e two volumes consist ent .

■ In synchronous mode, a write operation is not confirmed as c omplete u ntil the

remote volume has been updated. Synchronous mirroring forces the Sun SNDR software to wait until an ack no wledgement o f t he receipt o f the data is rece ive d from t he secondary by the primary before returning to the a pplication.

■ In asynchronous mode, a write operation is confirmed as complete b ef ore the

remote volume has bee n u p dated. Asynchrono us mirroring allows the Sun SNDR software t o return to the host as soon as t he write has been completed on the primary volume and been place d on a per volume queue for t he secondary sit e. Subsequently, the seco ndary site receives the queued requests in the order that they were queued. Once the I /O has been completed at the seconda r y site, notificatio n is sent to the primary.

In the event of p l a nned or unplanned outages, the Sun SNDR software maintains per-device scoreboard bitma p v olume s that are marked to indicate ch ang ed blocks with a granularity of 32 K bytes pe r se gme nt. T his t echniqu e allow s f or optimized resynchronizati on by allowing the Sun S NDR softwa re to resynchronize only the blocks that have changed.

OtherfeaturesincludedaspartoftheSunSNDRsoftwareare:

■ Grouping volume sets —TheSunSNDRsoftwareenablesyoutogroupvolume

sets. Grouping volume sets gua rantees write ordering. F or e xample, in a synchronization from the primary host to the secondary host, write operations to the secondary volumes in the group occur in the same order as the w rite operations to the primary volumes in the group.

You can also assign specific volume sets to a gro up to perform sndradm commands on these volume s ets and not on others you have configured. See “Order-Dependent Writes and Volume Set Grouping” on page 13.

Note – You can also group volume sets according to their cluster or resource tag to

perform replication in a Sun Cluster 2.2 or 3.0 Upda te 1 clustered environment o nly.

2 Sun StorEdge Network Data Replicator 3.0 Config uratio n Guide • June 2001

■ One-to-many and multihop volume sets — The Sun SNDR software enables you

to create on e-to-many and multihop v olume sets. In a on e-to-many v olume set , you can replicate data from on e p rimary volume to many secondary volumes residing on one or m ore hosts. In a multihop set, the secondary host volume of one volume set can be the primary h ost volume of an other v olume set. See “One-to-Many and Multihop Volume Sets” on page 18.

Supported Hardware and Software

Operating Environment Supporting Software

Optional Software

Supported Volume Manager Software

Host Types

Supported Attached Storage

TCP/IP Connection Hardware Components

The Sun SNDR software requires a TCP/IP connection between the primary and secondary server. Each server must have the proper ATM or Ethernet hardware installed to support the T CP/ IP link .

The Sun SNDR software operates over an y TCP /IP networking te chnology but has been qualified o nly on 10, 100, and 1000 Mbit Ether net and ATM 166 an d 622 technologi es.

Solaris™ 7 or 8 operating environment or subsequent compatible version Network tran sport software s uch as S un ATM™ or Giga bit Ethernet transports Sun StorEdge Instant Im age software Version 3.0; install thi s package for

additional point-in-time capability Sun Logical Volume Manager

Sun Solstice DiskSuite™ Veritas Volume Manage r

Server hosts using the Solaris operating environment and any Sun-supported network interface card. Hosts include:

• Sun Enterprise™ Server models 2x0 through 4x0

• Sun Enterprise Server models 3x00 through 10000 The Sun SNDR s oftware is storage-hardware independent

A dedicated TCP/IP link is not required.

Chapter 1 Overview 3

Network Multipathing

Network multipathing with failover is su pporte d on hosts running the Solaris 8 , Update 3 operatin g e nv ironment . T his feature is provided as part of the standard Solaris operating environment and is transparent to the Sun SNDR software.

The Sun SNDR software does not natively supp ort the functionality listed in

TABLE 1.

However, other Sun products can be use d with the Su n S NDR sof tware to provide these facilities.

TABLE 1 Sun SNDR Software Related Functionali ty

Functionality Sun Product

Network interface aggregation and network alternate pathing

Network encryption Network bandwidth allocatio n

Sun Trunking™ software and the native facilities provided in a Solaris operating environment update.

SunScreen™ Software Solaris Bandwidth Manager

4 Sun StorEdge Network Data Replicator 3.0 Config uratio n Guide • June 2001

Applications

The Sun SNDR software provides protection of critical enterprise info rmation. Th e following information types are cand idates for remote replication:

■ Database partitions and logs

■ Data that is important for b usiness continua nce in a disaster situation

The Sun SNDR sof tware can be leveraged for additional applicat ions, such as:

■ Data migration

■ Remote backup

■ Remote data analysis

■ Test and development

Archit ecture

The Sun SNDR software operates on log ical volumes th at can b e linear, striped, or RAID devices. You can create the logical volumes b y using the Sun Solstice DiskSuite™ or Veritas Volum e Man ager sof tware.

The core Sun SNDR software code i s a kernel mo dule that interfaces t o the network storage control module (NSCTL) data service framework. The Su n SNDR software is configurable on any device t hat is a ccessible th rough t he NSCT L data service framework. The sndradm CLI is the ex te rnal user interface us ed to man age the Sun SNDR software.

FIGURE 1 shows th e relationship between SN DR and the rest of the NSCTL data

service framework.

Chapter 1 Overview 5

Primary host

Secondary host

NSCTL -

Network storage

control module

Application

Sun STE or SV

Sun SNDR

Sun StorEdge Instant Image

SDBC

User Kernel

Sun STE or SV Sun SNDR

Sun StorEdge Instant Image

SDBC

Device driver

FIGURE 1 The Sun SN DR Software Architecture

Device driver

HardwareHardware

User Kernel

NSCTL Network storage control module

6 Sun StorEdge Network Data Replicator 3.0 Config uratio n Guide • June 2001

CHAPTER

Configu ra tio n Conside ra tions

Volumes Eligible for R eplication

Generally, includ e the following c ritical volume s in the Su n S NDR configu ration:

■ Database and database management system (DBMS) logs (the total database or

online DBMS log)

■ Access control f iles

You can exclude volumes from the Sun SNDR software configuration if they can be reconstructed at the recovery site or if they se ldom change:

■ Temporary volumes (such as those u sed in sort operations)

■ Spool files

■ Paging volumes

When selecting a volu me to b e us ed in the Sun SNDR software volume set, ensu re that volume does not contain d isk lab el privat e areas (for exa mple, slice 2 on a Solaris operati ng environmen t-formatted vol ume). The di sk label regi o n is contai ned in the first sectors of cylinder 0 of a disk. The safest method is to ensure that cylinder 0 is not part of any logical vo lum e t hat is replicated (excep t for v olume s un de r Veritas Volume Man age r cont rol, where cylinder 0 can be part of a logical volume that is replicated).

Choosing Volume Lev el Protection

In general, customers should protect their data with some level of RAID. With the Sun SNDR software, t he primary v olume s c an be protected by any software or hardware RAID level desired . The protectio n level of t he secondary v o l umes does not hav e to match that of the primary volumes. For example, if the primary volumes are R AI D1, t he secondary volumes could be RAID5.

Bitmap Volumes for Scoreboard Logs

Note – After ed i ting the /usr/kernel/drv/rdc.conf file, reboot your server.

The Sun SNDR Version 3.0 software does not support bitmap files.TheSunSNDR software uses regular raw devices to store bitmaps, used t o m aintain th e Sun SNDR scoreboard logs. For exam ple, you can specify a bitmap vo lume as

/dev/rdsk/c6t0d0s4.

Theserawdevicesshouldbestoredonadiskseparatefromthediskthatcontains the da ta. Configure RAID (such as mirrored partitions) for these bit map devices and ensurethatthemirroredmembersarenotstoredonthesamediskasthedata.

In a clustered environment, a bitmap must reside only on a volume. The bitma p volume in this case must be part of the same disk group or cluster resource group a s the corresponding primary or secondary d ata volum e.

A bitmap main tained on disk can persist across a system crash, depending on the setting of rdc_bitmap_mode in /usr/kernel/drv/rdc.conf. For example:

# rdc_bitmap_mode # - Sets the mode of the RDC bitmap operation, acceptable values are: # 0 - autodetect bitmap mode depending on the state of SDBC (default). # 1 - force bitmap writes for every write operation, so an update resync # can be performed after a crash or reboot. # 2-onlywritethebitmaponshutdown,soafullresyncis # required after a crash, but an update resync is required after # a reboot. # rdc_bitmap_mode=0;

8 Sun StorEdge Network Data Replicator 3.0 Config uratio n Guide • June 2001

If your server is configured in a clustered e nvironment , se t the bitmap mode to 1. If your server is not configured in a clustered environment, you can also choose the bitmap mode setting of 1 to improve error or disaster recovery.

Choosing a Connection M edium to L ink My Sites

The primary and se cond ary sites mus t be connected by a standard me dium that supports TCP/IP. For example, you can use any me diu m such as ATM, ISD N, Ethernet, Gigabit-Ethernet, or T1 and T 3 lin es to replicate data. Consider cost, bandwidth, a nd latency when choosing a connection medium.

The Sun SN D R software uses the maximum n etwork bandwid th avai l a bl e to it. I f the Sun SNDR software must share the network connection w ith other applications, y ou can use a bandwidt h allocator to restrict the bandw idth available to an application.

ATM Link Advantages

ATM is a standards-based high-perform ance WAN protocol tha t establishes routes at circuit initializat ion. Its pe rform ance, combined with SONET/SDH’ s rin g-healing resiliency, have made it the choice of carriers in their core backbone ne two r ks.

ATM Quality of Service parameters allow customers to choose the circuit characteristic s tha t best suit their needs and budget. They define how different WAN ports competing for ban dw idth should be prioritized relative to ea ch ot her, each having “virt ua l paths” through the netwo r k fabr i c. Voice, vide o , and LAN traffic ca n move over the same co nnection as cr i ti c a l remote mi r rori ng connect ions betw een primary and recovery site s. ATM switches m ake these varied protocol adaptations possible.

The Sun SNDR software will operate over any TCP/IP networking technology but has only bee n qualified on 10, 100, and 1000 Mbit Ethe rnet and ATM technolo gies.

Chapter 2 Configuration Considerations 9

Configuring Redunda nt Links Betwe en Site s

The Solar i s 8 operating environment off er s IP multipa thing. Thi s feature permi ts a Solaris host to group multiple physical n etwork interfaces int o a single logical interface . Redundancy between pa ths permits transparent opera ti o n in the event of a failure anywhere on the path inclu ding f ailures of ne twork interface ca rds, links, switches and routers.

This feature also provides the Su n SNDR software with the t ranspa rent m ean s fo r surviving link failures. It provides the ability to aggregate bandw idth across t he physical in terfaces permitting a pair of ATM 622 Mbit links to operate as one logical 1244 Mbit link with resiliency.

Link Sec uri ty

Solaris 8 operating environment offers IPsec, th e indu stry standa rd form of integrating encryption and au the ntication mechanisms into standa rd IP internetwo r king. A Solaris 8 host can authenticate and encrypt traffic on a conversation- by- c onversation basis.

Additionally, Su n offers SunS creen encryption and authentication of IP traffic. Coupled w ith t he Sun SNDR software, SunScreen s oftware can provide an ad ditional le vel of security to the d ata bein g transmitted between sites. Sun Screen software us es public key encryption technology to guaran tee tha t traffic is s trongly enc r ypted. The p ubl i c key mech ani sm is also used to authenticate that the sender of the traffic is the correct entity. SunScreen software i s normally configured at the edge of the d a ta center network. Of course, c o o perating SunScreen so f tware is required at each da ta center.

software tec hnology that perm its both

10 Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Choosing Betwe e n Synchronous and Asynchronous Replication

In synchronous mode, a write operation is not confirmed as c omplete u ntil the remote volume has been u pdat ed. G en erally, synchronous mirroring is limited to relatively s hort distances (that is, tens of kilom eters) because of the detrimental effect of round-trip propagation delay on I/O response times. However, there are applications such as web server replication that can tolerate relatively slow remote updates and operate in a synchronous mode over long st retches.

With synchronous mirroring, the remote copy alw ays matches the local host’s view of committed writ es. Should the local primary site be rend ered inoperative, the remote secondary copy can be used to conti nue o perations after the user community and the applications are sw itche d to the alternate site.

What if the link goes d own while run ning i n synchronous mode ? Sh ould the local I/O remain incomplete until the link come s back up? Some applications require that the primary and seconda ry sit es be e x actly in sy nc and therefore would desire that the I/O not co m plete. However, many mission-critical customers decide not to block local access to the data upon encountering intersite tr ansmission errors. Instea d, software keeps track of these writ es at the p ri m ary site and t hen updates the recovery sit e w hen the remote s ervice is reliably restored. If configured this way, disaster recovery procedures must take into accou nt loss of in-flight and logged data. That is, data might h ave been committed to th e local application but never had a chance to arrive at the backup site.

Asynchronous mirroring affirms primary I/O complet ion t o th e orig inating host before updati ng the remote image. This ty p e o f mirroring i s often used when the distance and relatively low bandwidth telecommunications lines of 45 Mbps or less between primary and se cond ary sites would introduce prohibitive latencies if performed synchronously. Here, t he long-distance pipe becomes the bottleneck, forcing local write s to be qu eued for later transmission. Consequently, there is a higher possibility of losing buffered and in-flight da ta if the primary system fails.

Chapter 2 Configuration Considerations 11

When To Suspend Replication to the Secondary Site

For many cust omers, the Sun SNDR sof tw are i s us ed to mirror the primary site’s information onto the altern ate location as q uickly as possible under the constraints of distance and technology. Operator e rrors, so f tware b ugs, and hardware data corruption are solid arguments for taking more de liberate, albeit less real-time, approaches to remote copies.

A deferred-write policy under such conditions delays remote updates until the local data has been confirmed to be good. The data integrity checks are performe d periodically, followed by th e remote copy. Some IT organizations reason that it is better to have slightly sta le, good data at the remote site t han to risk corrupt ing the remote copy with the lock-step updates. Co nsci o u sly scrutinized database r edo logs facilitate the recovery and upd ate process, while minimizing the consequences of the errors.

Another method i s t o ship th e da ta remotely in r eal time, take a snapshot of the dat a attheremotesitewithSunStorEdgeInstantImagesoftwareataknownpointin time, an d verify its integrity in the background before setti ng it asi de for recovery.

Telco cost s might similarly dictate a def erred copy p olicy. Some customers must timeshare n a r row pipes between sites during the peak process i ng hours, lea ving only off-hours for bulk intersite copies. Such prospects look for incremental update capabilities to reduce the transm ission load and copy time. In other words, they prefer to send only what ha s changed since the pre vious remote image was generated.

Configuring The Sun SNDR Softw are for Mutual Replication

Sometimes the distinction b etween primary ( A) and secondary (B) sites is blurred. As applications are geographically distribu ted, a secondary storage system at Site B might function as a remote volume replicat ion to Site A and as a direct storage resource for applications on Host B. Under these circumstances, you migh t also elect to have critical applications running on Host B to have their volumes replicated to Site A. This reciprocal replication arran gement supported by the Sun SNDR software is known as mut ual replication.

Each server can concurrently transmit and receive writes to and from its remote counterpart. Eac h system conta ins primary disks in a S un SNDR so f tware set that are acces sible by local hosts, as well as remote mirrors secondary to remote hosts. Mutual replication might be use d where critical ap plications and st orage are split across sites, and both sites require remote replicated volumes.

12 Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Order-DependentWritesand Volume Set Grouping

For the Sun SNDR Version 2.0 softw are, writ e o rder ing is only maintained by th e Sun SNDR software within a logical volu me. I n Version 3.0, write ordering is also maintained for groups of as ynchronously replicating volume s ets. ( The g eneral definition of write ordering here is that w rite operations directed to the target volume occur in the same order as write opera tions to t he source.) The group of target v olumes is a point-in-time copy of th e g roup of source volumes.

This feature is especially v aluable in those cases where you can avoid application requirements that limit operat ions. For example, a database app lication migh t limit partition sizes to no greater than 2 Gbyte s. In this case, you m i ght gro u p volume sets to create a virtual large “volume” that preserves write operations. Otherwise, you might risk having inconsistent d ata by trying t o update volume sets individua lly instead of as a group.

When an application h as multiple logical volumes assigned , ap plication data integrity can be maintained by one of the fo llowing:

■ Specifying all Sun SNDR software volumes associated with that application as

SYNC

■ Using Su n S torEdge Instant Image software to take periodic recover abl e

point-in-time copies

If you use Instan t Image software, the remote point-in-time is taken while the application is in the recoverable state. For example, most database applications allow for a hot backup. If a remote point-in-time copy were made of the entire replicated database while the primary w a s in hot backup mode, then a consistent remote database is available by using th e p oint-in-time copy and the log files taken while the database was in hot backup mode.

Chapter 2 Configuration Considerations 13

Recovery Consid er ations

The S un StorEdge Network Data Replicator 3.0 System Administrator’s G u ide contains information about various recovery scenarios. This section describes the following topics:

■ Failing Over to the Secondary S ite

■ Recovering the Primary or Se cond ary S ite

■ Using The Sun SNDR and Sun S torEdge Instant Image Software

Failing Over to the Secon dary Site

Should the primary site fail, the s econdary copy can be used to con tinue ope rations after t he user commun ity and the applications are sw i tched to the alternate site. You should im pl ement a ppl i c ation lev el recovery procedures at the secondary site to help ensure applicat i on r ec overy to a well-known stat e.

Recovering th e Primary or Secondary Site

Occasionally, remote mirroring operations are interrupted either intentionally or by unplanned outages. Normally, these i nterruptions are h andled by the S un SNDR software because whenever a member of a Sun SNDR software volume pair becomes unavailabl e, the write ac tivity is scoreboarded in the volume’s bitmap. When the service is restored, a fast update or resynchronization is performed.

14 Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Choosing the Resy nc hronization Type: Update or Full

Tip – If a synchronization i n itiated by the sndradm -m or

sndradm -m -r commands is interrupted, use the sndradm -m -u update

command to complete the synchronization. Use /usr/opt/SUNWscm/sbin/scmadm -S to view the synchronization progress.

An upd a te resynchroniz a ti on appli es changes that occur red at the primary data to thesecondarysiteduringthetimereplicationwassuspended.Theprimarysitecan also be updated from t he secondary, if desired.

A full synchronization is a com plete d isk-to-disk copy. This operation is the most time consuming of the s ynchronization o perations. A full sy nchronization is only done when the Sun SNDR software volume set is:

■ Initially established

■ Damaged due to a disaster

■ Data integrity is questions

If the integrity o f the Sun S N DR software volume data is questioned, then the only way to get the volume back into a synchronized set is to perform a full volume copy.

The Sun SNDR software volume set data might be in question if, for example, th ere was a d ouble disk failure on a RAID 5 set or if the Sun SNDR software is shutdown manually and writes occurred to eith er t he primary or secondary volumes without scoreboarding being active. Th e full copy can e ither be p erformed from the primary to t he secondary or if appropriate, from the s econdary to the primary.

Choosing Automatic or Manual Res yn chronization

The Sun SNDR software provides a ch oice of automatic or manual resynchronization after a disaster. Automatic resynchronization is discouraged if the interruption is the warning of a larger rolling disaster. It is best t o main tain the sec ondary s ite in a dated but cons i s tent state, rathe r than risk a disastrous interruption that leaves the secondary inconsistent and difficult to recover f rom. The autosynchronization option is disabled by default for this reason.

See also “Using T he Sun SNDR and Sun StorEdge Instant Image Software” on page 16. Before you start a resyn chronization operation, ensure that you have an appropriate Instant Image software point-in-time copy of the Sun SNDR software target vol u m e.

Chapter 2 Configuration Considerations 15

Using The Sun SNDR and Su n Sto r Edg e Insta n t Image Software

To help ensure the highest level of data integrity on both sites during normal operations or during data recov ery, use the Sun SNDR software with the Sun StorEdge Instant Image software.

The Instant Image software is best used just before you perform a resynchronization, to help ensure that a consistent copy o f data exists. In this case, if the resynchronization is interrupted, you a t least have a copy of known good data that is usable.

During the resynchroni za tion process of updating the local and remote sites, the data on a se cond ary Sun SNDR volume is tempo rarily inconsistent with th e primary volume. T he secondary volume cannot be relied on for da ta recovery. Consistency is restored when the resynchronization is co m pl ete. To help ensure data integrity, use Instant Image software regularly to create a point-in-time copy of data at both sites. See the Inst a nt I m age docu mentation listed in “Related Docume ntation” on page vii.

When to Use The Sun StorEdge Instant Image Software at the Remote Site

In most cases, customers should also install Instant Image software at the secondary site t o protect against a d ual f ailure. Before you resynchronize the primary site with the secondary, take a point-in-time snapshot c o p y of the data. If f ailure the occurs during the resynchronization, you have the point-in-time data copy to roll back to andyoucanstartagainwhenitssafetodoso.

Whenever a fast resynch ronization is being perfor med, the I /O transfer is i n block order, not in I /O order. Therefore the v o l um e being resynchronized will not be consistent until the fast resynchronization has been completed and the volum e is back in replicating mode. If a point-in-time copy is not availab le at the remote sit e, then the remote site recovery plan should c over t he exposure that will e xist d uring the time required to per f o r m the fast resync hro ni zation.

Additionally, a point-in-time sn apsh ot at the second ary site can be used for applications such as remote backup, remote data an alysis, or other functions.

16 Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Sun SN DR Software and Sun StorEd ge Fast Write Cache Software

Note – You cannot use the Sun S torEdge Fast Write Cache (FWC) prod u c t, inclu ding

the SUNWnvm Version 3.0 software, in a Su n Cluster env i ronm ent because cache d data is inaccessible from other machines in a cluster. To compensate, you can use a caching array, such as the S un StorEdge A3500 disk array.

The Version 2.0 a nd Version 3.0 Sun StorEdge data s ervices are binary incom patible. If your system in cludes Version 2.0 of the Sun St orEd ge Instant Image (including Instant Image 2.0.1 with STE 1. 2), S un SNDR software, o r Sun StorEdge Fast Write Cache, you must remove them befo re in stal l ation. For example, you c annot use Sun StorEdge Instant Image software Version 2.0 with Sun SN DR software Version 3.0. When you plan to install or upgrade to a Version 3.0 data service, you must remove all Version 2.0 and 2. 01 data services.

However, the Sun StorEdge Co re Services Version 3.0 Software CD contains th e Sun StorEdge SUNWnvm Version 3.0 software package f or those u sers whose systems include Version 2.0 of the Sun FW C hardware and software product and who wish t o continue using the Sun FWC produc t.

For optimum performance in a noncluster environment, you can use the Sun SNDR software wi th the Sun StorEdge Fast Write Cache SUNWnvm Version 3.0 product on the primary and seconda ry sites f or t he volumes conta ining bitm aps and any other volumes for which wr ite p erform ance is critical (for example, database log files). Using th e FWC product allows the scoreboard to be preserved across a sys tem crash without adversely affecting performance d urin g replication.

Chapter 2 Configuration Considerations 17

One-to-Many and M ultih op Volume S e ts

The Sun SNDR softw are enables you to create one-to-ma ny and multihop volume sets.

In a one-to-many volume set, you can replicate data from on e primary volume to many secondary volumes residing on one or more hosts. One primary and each secondary h ost v o lume is a single volume set (ea ch secondary volume requires its own unique secondary bi tmap volume). When you perfor m a forward resynchronization, you can synchronize one volume s et or all v olume sets; in this case, issue a sepa rate command for each set. You can also update the primary volume by using a specific secondary volume. three second a r y host volum es and therefore thr ee volume sets: A and B1, A and B2, and A and B 3.

Note – You can group on e-to-many se ts that sha re a comm on p rimary volume in a

single I/O g roup to operate on all set s simultaneously instead of issuing a separate command for each set. See also “Order-Dependent Writes and Volum e Set Grouping” on page 13.

In a mult iho p s et, the se c ondary host volume of one v o l ume set ca n be the pr im ary host volum e of another volume set.

FIGURE 1 sh ows one primary a nd one secondary

host volume; the secondary host volume B becom es the primary h ost volum e A1 to the seco ndary host volume B1.

FIGURE 1 shows o n e primary and

One-To-Many

Primary host volume

/dev/rdsk/c0t0d0s5

Multihop

Primary host volume Secondary host volume Secondary host volume

/dev/rdsk/c0t0d0s5 /dev/rdsk/c0t0d0s5/dev/rdsk/c0t0d0s5

One volume set Another volume set

FIGURE 1 One-to-Many and Multihop Volume Sets

18 Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Secondary host volume

/dev/rdsk/c0t0d0s5

Secondary host volu me

/dev/rdsk/c0t0d0s7

Secondary host volume

/dev/rdsk/c0t0d0s9

A = Primary host volume B = Secondary host volum e

Using The Sun SN D R Software i n a Firewall E nvironment

You can use the Sun SNDR software wit h any enh a nc ed net wo r k product that Sun offers. Port 12 1 must be available for use b y t he Sun SNDR sndrd daemon.

You can use IP masquer ading. SNDR uses conn ec ti o n- o r iented service (COTS) based remote proced ur e c al l s (RPC; that is, TCP). T he RPC part of the packet does not contain any add res s informatio n.

Chapter 2 Configuration Considerations 19

20 Sun StorEdge Network Data Replicator 3.0 Configuration Guide • June 2001

Sun Microsystems StorEdge Network Data Replicator 3 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Contents

Preface

Before You Read T his Book

Using UNIX Commands

Documentation Conventions

Shell P romp t s

Related Documentation

Accessing Sun D ocume nta tion Online

Ordering Sun Do cumentation

Sun Welcomes Your Comments

Overv iew

Sun SNDR Software Description

Supported Hardware and Software

TCP/IP Connection Hardware Components

Network Multipathing

Applications

Archit ecture

Configu ra tio n Conside ra tions

Volumes Eligible for R eplication

Choosing Volume Lev el Protection

Bitmap Volumes for Scoreboard Logs

Choosing a Connection M edium to L ink My Sites

ATM Link Advantages

Configuring Redunda nt Links Betwe en Site s

Link Sec uri ty

Choosing Betwe e n Synchronous and Asynchronous Replication

When To Suspend Replication to the Secondary Site

Configuring The Sun SNDR Softw are for Mutual Replication

Order-DependentWritesand Volume Set Grouping

Recovery Consid er ations

Failing Over to the Secon dary Site

Recovering th e Primary or Secondary Site

Choosing the Resy nc hronization Type: Update or Full

Choosing Automatic or Manual Res yn chronization

Using The Sun SNDR and Su n Sto r Edg e Insta n t Image Software

When to Use The Sun StorEdge Instant Image Software at the Remote Site

Sun SN DR Software and Sun StorEd ge Fast Write Cache Software

Using The Sun SN D R Software i n a Firewall E nvironment